Mechanical couplings have been used for a variety of applications. In particular, such couplings have been connected to (i.e. joined to, united to or linked with) various substrates including cables which have then been terminated or connected to other cables and the like. Such couplings have been used, for example, in connection with CATV cable. There are various types of CATV cables. It is particularly advantageous to use two particular types of cables with this invention. The first type of cable (Type-I) includes a center conductor surrounded by a dielectric, a rigid outer conductive wall defining a shielding means surrounding the dielectric and a protective jacket surrounding the outer wall. In some of the newer more flexible cables of this type, the protective jacket is polyethylene and is bonded to a thin outer wall such that the jacket cannot be removed or stripped from the outer wall without damaging the thin wall.
The second more flexible type of cable (Type-II) includes a center conductor surrounded by a layer of dielectric material, which is surrounded by an EMI foil shield, which is surrounded by an electrically conducting braid (also for EMI shielding purposes) and which is surrounded by a protective jacket. Quite often there are multiple layers of foil and braid.
A presently used typical coupling for Type-I cable is a threaded coupling having two outer members which are threaded to one another and sealed by means of an O-ring. The coupling also includes two inside members, each having a tapered inside surface. The inside members grip the wall deforming it to a smaller diameter such that a split ring between the inside members grips the wall at the deformed portion. O-rings are used to seal the inside and outside members.
A presently used typical coupling for Type-II cable includes a connector body having one end adapted for insertion in the cable between the EMI foil shield and the EMI braid. A narrow ring is positioned around the protective jacket adjacent the area of the cable to be connected to the coupling. A separate crimping tool is then positioned around the ring and crimped by applying pressure to the tool. The ring is distorted by the pressure and clamps down on the cable and connector body.
Certain disadvantages have been noted in using the typical coupling for Type-I cable. The typical Type-I coupling for such cable is craftsman-sensitive. Once the coupling has been installed on the cable, the coupling must be tightened to a predetermined torque level for good electrical properties between the coupled cable and a joint such as a connection with other cable or termination to a tap box or the like. If the connection between coupling and cable is overtightened and there are corrosive substances present stress cracking may result. Undertightening will cause poor EMI shielding and cable pull out under wind, ice or thermal loading conditions.
Additionally, typical Type-I and Type-II couplings are craftsman-sensitive because they require a portion of the protective jacket to be stripped back before connection with the cable. If the stripping operation is done incorrectly, portions of the electrical conductor or aluminum foil shield or braid shield may be lost and the cable's electrical properties damaged.
The stripping-back operation of both the Type-I and II cables destroys, inherently, some of each of the cable's environmental protection, i.e. the protective jacket at a particular crucial point, namely the connection or termination point of the cable. The stripping-back operation also slows down the craftsman. He must not only do the job, but he must do it with some degree of delicacy, so as not to destroy the cable's electrical properties or an unnecessary amount of its environmental protection.
Additionally, Type-II cables are often crimped incorrectly. The foil and braid are bunched together or destroyed, decreasing the EMI shielding properties of the cable.
Such cables are generally exposed to the harshest of outdoor environments at the connection or termination point. Such conditions include temperature changes of 100.degree. F. or more within a 24 hour period. Additionally, the connection or termination must be able to withstand rain, ice, snow, extreme heat and cold, ultraviolet radiation, oxidation, pollution and salt spray without damage.
Additionally, the connection between the coupling, cable and termination or connection must be secure enough to prevent the wind from loosening same. The wind will cause vibration along the cable line and typically loosen the connection between coupling and cable and between coupling and the joint, such as termination or connection point.
The terminated or connected cable must be sealed so that it does not leak electromagnetic radiation, also known as electromagnetic interference (EMI) or radio frequency interference (RFI). Such EMI causes disruption of aircraft instruments, radar and the like and has become a deep concern for certain federal and state government agencies.
Typical Type-I and Type-II couplings fail to provide either adequate environmental seal or EMI seal. The result is that the coupling and/or termination and connection must be replaced quite frequently. Additionally, poor EMI shielding interferes with the electrical performance of aircraft instruments, radar and the like.
The tolerance limits for typical CATV cable are quite broad. For example, a typical 1/2" Type-I cable diameter varies from 0.493 to 0.507. A typical Type-II cable diameter varies from 0.234 to 0.250 for a RG59U cable. Typical couplings cannot presently handle such wide tolerance ranges.
A specific example of a typical Type-II coupling is disclosed in O'Keefe, U.S. Pat. No. 3,551,882 which is a crimp-type coupling for multiple outer conductor coaxial. A malleable ferrule is crimped down onto the inner braid to terminate it to the connector and an outer ferrule is then crimped down onto the outer braid directly over the inner ferrule to join it to the coupling. An example of a Type-I coupling is disclosed in Blanchard, U.S. Pat. No. 4,346,958 which uses O-rings to provide an environmental seal. Due to the broad tolerances of cable diameter, as mentioned above, it is difficult to achieve satisfactory seals with O-rings. Other examples of coaxial cable connectors are disclosed in Hyslop, U.S. Pat. No. 3,336,563 and in Hayward, U.S. Pat. No. 4,400,050.
Additionally, a heat-recoverable coaxial coupling assembly is disclosed in copending U.S. application Ser. No. 531,961 filed Sept. 14, 1983 for Type-I cable which includes a connector body having a mating area and a driver member made from heat-recoverable material surrounding the mating area. The cable jacket is positioned between the mating area and the driver member. The driver member is then heated to effect recovery. As the driver recovers it deforms the cable jacket at the mating area to prevent pullout of the cable and forms environmental and EMI seal. While quite effective at eliminating many of the above-described difficulties, such coupling assembly does require the use of heat. There are circumstances when heat, especially in the form of a flame, is undesirable.